Update: Well today I met the DoP and Director at the rental house and we gave it a try, it reminded me of playing Buckeroo as a kid, adding one bit at a time and waiting for it to go twang. We stripped off everything we could, from the EVF eye piece, mic holder etc, fitted a small Sony battery, 1 S*S card and single lightweight rail for the motor, powered from the rig. To my surprise it didn't bottom out the arm but it was heavy. The post had to be set full length making it very cumbersome but I got it balanced and actually I still have a couple of little bits in reserve which I can remove, 1 small weight, the quick release plate oh and the rubber band. The fully loaded sled weighed just under 16lbs, I believe the maximum is 15lbs but the arm hung just below level. I suppose I was hoping for it to bottom out the arm so they could easily see it was over weight.
I am more concerned now about damaging the gimbal and having to boom up just to get headroom. I think the latter will be what actually convinces them to pay a bit more for the upgrade as I think they realise it is only going to compromise the performance and maybe wreck the shots they want. I have now agreed to take both the Pilot and the Archer on set so that we have both options.
What do people think are the chances of the gimbal bearings disintegrating during an 8 day shoot, almost a pound over weight?